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No more polluted caches!

Why it happens, and how to stop it.

Cache pollution occurs in Windows when incorrect DNS responses fill your DNS server's cache with responses from domains other than the one the DNS query itself requested. For example, if you requested a domain and the referral returned the address of, that reference will be stored in your DNS cache. Multiple referrals might be returned, but this sort of thing not only is frustrating to users in that it sends them to the wrong site, but it clogs up the arteries of your DNS server making requests take longer than necessary to be returned.

In most cases the default behavior is to store referrals, and that's not a problem for small systems serving a few users. However, for large networks, or those that require optimal performance, you will want to get rid of any referrals that are from a domain other than the one requested. This option in the Window DNS Server is called Secure cache against pollution (an apt term) and it's found in the DNS Properties dialog box as a check box that you need to enable.

Here's how you get to it:

  1. Open the DNS Management console in the MMC
  2. Right click on the DNS server of interest and select the Properties command.
  3. Click on the Advanced tab, then click on the Secure cache against pollution check box.
  4. Click OK to save your setting.

Barrie Sosinsky is president of consulting company Sosinsky and Associates (Medfield MA). He has written extensively on a variety of computer topics. His company specializes in custom software (database and Web related), training and technical documentation.

This was last published in November 2003

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